| 摘要 |
<p>PURPOSE:To reduce the amount of return oil as well as save the consumption of energy by a method in which an oil path closing means to interrupt the supply of pressure oil to the rod side oil chamber of a cylinder from a direction switch valve is provided, and a bypass through which pressure oil coming from an oil-pressure pump flows to a tank at the switching position on the contraction side of the cylinder is provided to the direction switch valve. CONSTITUTION:In the case of boom lowering, a signal is generated in a pilot pressure signal circuit (f), by which direction switch valves 33 and 20 for boom are switched to a switching position Y on the contraction side of a cylinder. Also, pressure oil from the main oil pressure pump 10 returns as it is to a center bypass 35 through a bypass 36 and flows toward a tank. Then, only the pressure oil of the main oil pressure pump 11 is supplied to the rod side oil chamber 2A of the boom cylinder 2 through the direction switch valve 20 for boom, and return oil from the bottom side oil chamber 2B is dividedly flowed to the direction switch valves 33 and 20 for boom and returned to the tank. By this, the consumed electric power of the main oil pressure pump 10 can be reduced.</p> |
